Nitric Oxide Synthase: Difference between revisions

<scene name='Sandbox_5/Nos_oxygenase_bh4/11'>H4B</scene> is an essential cofactor in NOS and in the aromatic amino acid hydroxylases. NOS contains two molecules of <scene name='Sandbox_5/Begge_h4b/1'>H4B</scene>, one in each monomer. The active site forms part of the cavity already described. This cavity can be visualized as a <scene name='Nitric_oxide_synthase/Substratebinding_distal_pocket/2'>tunnel</scene>. Here H₄B helps substrate interactions by lining the active-center tunnel and hydrogen bonding to the heme propionate and to alfa helix 7. The propionate group and alpha helix 7 are also involved in the L-Arg binding. This gives H₄B the opportunity to play an important role in the control of subunit interactions and active site formation. H₄B is therefore more or less a structural cofactor and has a stabilizing effect. Its structural importance is further reconned to play a role in dimer formation (dimerization requires bound zinc ion along with H₄B), and major conformational changes leading to the formation of the active site channelform<ref name="Raman">PMID:9875848</ref>.